Already during World War II, polymers, generally hydro-soluble, were used to stabilize the soil. As early as the 50s, the scientific literature describes the use of various soil conditioning polymers including Krilium® by the Monsanto Chemical Company.
Many other polymers were then described for soil conditioning:                Synthetic polymers: for instance polymers and copolymers based on acrylamide, acrylic acid, acrylates, methacrylic acid, acrylonitrile, vinylpyrrolidone, vinylformamide, itaconic acid, vinyl acetate, maleic acid, ethylene glycol and derivatives of these polymers, for instance hydrolyzed polyacrylonitrile, alcohol polyvinyl, etc.        Natural polymers, natural rubbers, polysaccharides and their derivatives: galactomannan, guar gum, carob gum, xanthane gum, arabic gum, chitosan, carrageenan, pectines, starch, modified starch, alginates, celluloses, cellulose derivatives (cellulose ethers), agar-agar, etc.        Grafted polymers: for instance, acrylamide starch and acrylate copolymers, starch and acrylonitrile copolymers, chitosan and acrylic acid copolymers, etc. Among these polymers, high molecular weight polyacrylamides came under specific investigation and were adopted for soil conditioning, because of their efficiency and lower cost. In 1999, polyacrylamides were being used on more than 400,000 hectares in the United States, essentially by gravity irrigation.        
Acrylamide-based polymers incorporated into water are a way of drastically limiting erosion. Lentz et al applied doses of between 1 and 20 ppm of polyacrylamide to irrigation water (furrow irrigation) obtaining up to 97% decrease in erosion for a dose of 10 ppm. There is a great deal of literature on the subject and reference can also be made to the Lentz article, R. D., Shainberg, I., Sojka, R. E., & Carter, D. L. (1992): “Preventing irrigation furrow erosion with small applications of polymers” in the Soil Science Society of America Journal, 56, 1926-1932.
Not only do polyacrylamides limit hydraulic erosion but also the erosion caused by wind. That is why they are also used for controlling dust.
By avoiding the redistribution of fine soil particles under the effect of irrigation water or rain, polyacrylamides prevent slaking crusts from forming, causing the blocking of the soil pores and forming a waterproof and airproof crust. Small plants find it difficult to work their way through the crust, limiting crop emergence. Seed emergence can also be improved by the application of polyacrylamide.
The capability of polyacrylamides to limit water percolation in some soils and at some doses is used to limit losses in water conveyance canals. Soil erosion and in-depth water percolation cause the transfer of various pollutants. Applying polyacrylamide limits the transfer of nutrient elements, phytosanitary and pathogenic products.
The flocculation capability of polyacrylamides also reduces water turbidity in flooded crops.
Polyacrylamides also offer a wide range of benefits linked with soil conditioning in many different domains. But they can only be applied to the soil during irrigation periods, often considered to be an issue.
The application of hydro-soluble polymers such as polyacrylamides essentially takes place through irrigation systems: gravity irrigation, mechanical irrigation, drip irrigation. Polymers, usually in powder form, are thus dissolved and diluted at a rate of between a few ppm and several tens of ppm in irrigation water.
The transport vector is water but it has to be used in large quantities, confining the application of polymers to irrigation periods alone. Hydraulic sowing methods are sometimes used for applying polyacrylamide to the soil. The polyacrylamide is diluted in a large quantity of water applied to the soil. Accordingly, it concerns irrigation which, by definition, is limited to farmland, and is sometimes undesirable.
In the patent FR 2,798,818, the applicant proposes to use polyacrylamides to limit the soil tare level of tuber plants. However, there is no simple method of applying polymers other than to use an irrigation system. Therefore, if the user does not have an irrigation system or does not want to use it to limit the water content in the soil before pulling up, the application of polyacrylamide becomes an issue.
In other words, the conditioning of the soil must be carried out independently of the irrigation.
The document FR-A-2370430 describes a soil conditioning process which consists in applying to the soil a polymer solution (between 0.05 and 1% solid) therefore requiring a large amount of water.
But much of the soil to be conditioned is not farmland and it is unthinkable to waste enormous quantities of water to apply a conditioning polymer to the soil.
Alternatively, the idea of spreading the powder directly on the soil to be treated has been considered. The low density (approximately 0.8) of polyacrylamides or other polymers in powder form, makes the product sensitive to the wind. Applying a limited amount of powder per unit of surface area (less than 250 kg/hectare for instance) generates an application that is not uniform. In addition, the polymer is not in close contact with the soil particles and has to be “activated” by the rain or by irrigation water before becoming effective. Once it has been dissolved by rainwater or irrigation water, the polymer may still not be spread satisfactorily, because of its low mobility through the soil.
Other methods require the use of other vectors.
In the publication by Yu et al “Infiltration and erosion in soils treated with dry PAM and gypsum”—Soil Science Society of America Journal, 67(2), 630-636 (2003), the authors propose to resolve the problem of the quantity of water by using a filler: gypsum. More specifically, they mix polyacrylamide in powder form with quarry gypsum. The mixture is spread on the ground and the combination improves the performance of the gypsum. However, it decreases the performance of the polyacrylamide to reduce erosion and also involves the implementation of an amendment, preventing the application of this method in situations where this amendment is considered undesirable.
In the U.S. Pat. No. 7,503,143 by ENCAP LLC, it is proposed to fix the polyacrylamide to a solid vector, for instance a paper-based mulch. The product is then spread on the soil. However, this method leads to increased manufacturing, storage and transportation costs. The soil coverage continues to be mediocre once the product has been spread, found in the form of large granules spread out randomly on the surface. Accordingly, once the commercial product has been spread, the polyacrylamide is not directly in contact with the soil but is still fixed to its vector. This solution is not satisfactory.
US document US2011/0309170 describes a device for spraying either solids (FIG. 1-3), or liquids (FIG. 4). US document U.S. Pat. No. 2,888,206 describes a rotary support for liquid spraying, more particularly herbicidal compositions.
None of the solutions of the prior embodiment proposes a satisfactory method for applying to the soil such soil conditioning polymers as, for instance, polymers based on acrylamide.
Accordingly, the current solution continues to resort to irrigation. More specifically, irrigation water today is still the essential vector for applying soil conditioning polymers.
This means that there is a need for a new method of conditioning soils with hydro-soluble polymers, without having to resort to an irrigation system.